Exhaust gas turbochargers are widely used to compress supply air to an engine by exhaust gas of the engine to improve the output of the engine.
In a case of a common turbocharger (having one exhaust gas introducing passage), the supply air is likely to be insufficiently compressed in a low-speed rotation region of the engine, and as a countermeasure, twin-scroll turbochargers are employed.
A twin-scroll turbocharger has two separated exhaust gas introducing passages to a leading edge of a rotor blade in the turbine housing, one on the front side and the other is on the rear side.
Since such a twin-scroll turbocharger is capable of utilizing dynamic pressure of exhaust pulse of an engine, it has better performance than a usual turbocharger also in a low-speed rotation region of an engine.
In order to effectively utilize dynamic pressure of exhaust pulse of an engine, in a case of a four-cylinder engine, taking the order of the cylinders into consideration, exhaust pipes of the first cylinder and of the fourth cylinder are coupled to introduce exhaust gas into the rear scroll, and exhaust pipes of the second cylinder and the third cylinder are coupled to introduce exhaust gas into the front scroll, and the turbocharger is configured so that exhaust gas is introduced alternately into the front scroll and the rear scroll, and intermittently during two cycles of the engine.
However, when the flow from the front scroll and the flow from the rear scroll are switched, there is a period of time in which the flows from the both scrolls are introduced into the rotor blade, and thus the inlet of the rotor blade has a shape which is suitable for such a state. That is, because exhaust gas is introduced from the both scrolls into the rotor blade, the inlet of the rotor blade has an enlarged width (flow passage area).
Therefore, in the vicinity of the inlet of the rotor blade, exhaust gas blown from the outlet of the rear scroll is rapidly expanded, and the flow of the exhaust gas becomes turbulent, and such turbulent flow may generate swirling flow when it flows between fins of the rotor blade, whereby the flow resistance may be increased and the rotating force of the rotor blade is reduced, which may leads to a problem of reduction in efficiency of the turbocharger.
Prior art of the above feature includes the disclosure of JP H2-83304 U (Patent Document 1).
Patent Document 1 discloses a technique where a partition (scroll throat) separating a front scroll and a rear scroll has a guide plate thereon to adjust the direction of a flow of exhaust gas flowing in the vicinity of the partition.
By this guide plate, the flow angle of the exhaust gas is forced to change to improve the rotating force, thereby to improve turbocharging efficiency of the turbocharger.